Analysis on oscillations between two generators in a hydro power plant and development of math model for a compound excitation system

Xiping power plant (located in Guangxi, China) was restricted for only one unit running, whenever the second one was brought into the line, serious oscillation occurred between those two generators, and between the plant and the grid. A math model for the special exciter in this plant is developed in this paper. The exciter´s two DC outputs proportional to the stator current and voltage respectively are paralleled. The eigenvalue studies using the extended multi-machine Phillips-Heffron model and the exciter model show that the oscillation is caused by the current source of the exciter. The oscillation can be eliminated by a dynamic correction scheme in the AVR. As a result of this study, complete math models for this plant including the exciter and its reactive current compensation and an analysis method have been developed. The consistency of the results with the field tests demonstrates the validation of the models and method developed in this paper.